Methods of Making Purified Water from the Fischer-Tropsch Process

ABSTRACT

The Fischer-Tropsch (FT) process creates significant amounts of water. This FT produced water contains significant amounts of organic impurities. The invention provides methods of treating FT produced water. Surprisingly, it was discovered that the FT produced water could be successfully treated in a membrane bioreactor (MBR) according to relatively simple and more efficient steps; for example, by adjusting the pH of the water in the range of 4.2 to 5.8 or treating the FT produced water in a stripper where the distillate product stream and a reflux stream returning to the stripper have the same composition. In a related aspect, water compositions are described.

RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.14/855,327 filed Sep. 15, 2015, and also claims the benefit of U.S.Provisional Patent Application Ser. No. 62/050,753, filed 15 Sep. 2014.

INTRODUCTION Exploration Wastewater

Oil exploration produces the largest volume of wastewater in thepetroleum industry. This effluent, “produced water” (PW), results fromthe use of environmental waters such as seawater to displace the oil inthe reservoir. See Table 0-1. PW contains many different chemicalspecies which are onerous with respect to either their environmentalimpact or to abstraction operations, and technologies for theirtreatment are governed by a number of factors. Footprint is one of theimportant considerations when selecting treatment technologies. Forinstance, onshore installations where footprint is not critical, therelatively low-energy, simpler, high-footprint technologies can beemployed. This may include the same biological treatment technologiescommonly applied to other industrial effluents, including refinery andpetrochemical effluents.

The ranges of concentration of the key constituents vary widely, andgenerally the exact composition with reference to the additives is notknown and/or considered proprietary by the industry. Thus, whilst thebiodegradability of the mineral oil components can be quantified,assessment of biodegradation of the additives can be challenging. Theapplication of membrane bioreactor (MBR) technology to actual PWwastewaters (Table 0-2) appears to be still at the development stage(Kose et al., 2012; Pendashteh et al., 2012, Sharghi et al., 2013).

TABLE 0-1 PW quality from oil fields and gas fields, all in mg/L otherthan pH (Fakhru'l-Razi et al., 2009) COD BOD TSS TDS N—NH₄ pH Cl Ca HCO₃⁻ O&G^(a) Phenol Oil Min — — 1 — 10 4.3 80 13 77 2 0 Max 1,220 — 1,000 —300 10 200,000 26,000 4,000 565 23 Gas Min 2,600 75 8 2,600 — 3.1 1,4009,400 — 2 — Max 120,000 2,900 5,500 360,000 — 7 190,000 51,000 — 60 —^(a)O&G oil and grease

TABLE 0-2 Summary of MBR performance for treatment of petroleumwastewaters (Lin et al., 2012) OLR F:M % Flux Bioproc. V_(reactor)COD_(in) kgCOD/ HRT SRT kgCOD/ MLSS T rem Feed Membrane LMH config Lkg/m³ m³ · d h d kgVSS · d g/L ° C. COD Reference PW iHF, 0.1 μm 10 Ae5.1 1.5- 13- 2.7^(b) 30- 0.25- 2- 20 67- Kose et 3 26 “inf” 0.45 1683^(a) al., 2012 PW PVDF sMT, 75- Ae SBR — 0.56- 0.28- 24- “inf” 0.15-1.6- 30 97- Pendashteh et analogue/ 200 kDa 95^(e) 6.8 3.4 96 0.57 7.999^(c) al., 2012 real Petro- PVDF iHF, 10- Ax/Ae 2,000/ 0.074- 0.08-10.7- 50- 0.042- 3.0- 69- Di Fabio chemical 0.04 μm 18 2,200 0.223 0.5018.3 90 0.11 4.8 87 et al., 2013 Petro- iFS chlorin. 10- Ax/Ae 18/0.720- 0.9- 13- 25 0.12- 8.6- 26 85- Qin et chemical PE, 0.4 μm 12.5 301.59 3.0 16 0.23 9.6 95^(d) al., 2007 Refinery Ceramic 50- Ae 20 0.37-0.024- 17- — — 3- ~94 Rahman & Al- sMT, 0.2 μm 120^(e) 2.3 0.067 34 5.5Malack, 2006 Refinery iHF 15- Ae 4.4 0.4- 0.74- 10.0 “inf” 0.27- 2.1-~25 41- Viero et 17.5 1.05 1.72 0.77 10.4 67 al., 2008 Refinery iFS PVDF— An/Ax/Ae — 0.072- — — — — — 13- 89- Zhidong et 0.08 μm 0.296 17 98al., 2009 Oil-water sMT PVDF 40- Ae 11 0.5- 0.82- 6.7- — 0.26 ± 2.5- 3593- Scholz and analogue 15 kDa 100^(e) 3 9.82 13.3 0.54 g 30 98^(f)Fuchs, 2000 PW iFS chlorin. — Ae 0.75 0.6- 0.3- 48 80 — 1.1- 30 75-Sharghi et PE, 0.4 μm 1.8 0.9 5.2 95 al., 2013 ^(a)Generally 80-85%independent of COD_(in) ^(b)Calculated from other reported data inpublication ^(c)Decreases to 90% on increasing salinity from 35 to 250g/L ^(d)Insignificant impact of HRT between 13 and 19 h on COD_(out)(40-65 mg/L) ^(e)Highly dependent on membrane fouling condition, TMP andCFV ^(f)Other than at lowest OLR of 0.82 when removal was 77% OLROrganic loading rate HRT Hydraulic retention time SRT Solids residencetime F:M Food/micro-organism ratio MLSS Mixed liquor suspended solidsconcentration chlorin PE Chlorinated polyethylene PVDF Polyvinylidenedifluoride Ae Aerobic Ax Anoxic An Anaerobic iFS Immersed flat sheet sMTSidestream multi-tube iHF Immersed hollow fibre “inf” “infinite“ (nosludge wasting: SRT determined by sludge sampling)

Refinery Wastewaters Refinery Wastewater Origins

Refineries use hydrocracking, hydro-treatment and thermal distillationto generate products from crude oil. Wastewater sources from therefining process include tank bottom draws, desalter effluent, sourwater and spend caustic. These vary in composition both with respect totheir origin and with time (Table 0-3).

Entrained water in the crude derives from the oil well extractionprocess and/or from ingress during transportation. It is typicallyremoved as storage tank bulk solids and water (BS&W) or in the desalter,a key component of crude oil refining, and forms part of the wastewater.A significant effluent stream derives from where pre-softened orstripped sour water has been in contact with hydrocarbons. Wastewatersgenerated from operations from where no direct contact with hydrocarbonsarises include residual water rejected from boiler feedwaterpre-treatment processes: water produced from (i) regeneration of ionexchange resins in zeolite softeners and demineralisers, and (ii)blowdown (the concentrate stream) from cooling towers and boilers. Thereis also likely to be minor contamination of storm waters from run off,as well as minor flows from laboratory discharges, washing and sewage.

TABLE 0-3 Refinery effluent stream water quality, mg/L (IPIECA, 2010)Stripped sour Cooling tower Parameter BS&W^(a) Desalter water blowdownCOD 400-1,000 400-1,000 600-1,200 150 Free HCs Up to 1,000 Up to 1,000<10  <5 SS Up to 500 Up to 500 <10 Up to 200 Phenol — 10-100 Up to 200 —Benzene — 5-15 negligible — Sulphides Up to 100 Up to 100 — — Ammonia —Up to 100 — — TDS High High Low Intermediate ^(a)Tank bottom basicsediment and water

The principal water stream in a refinery is the cooling water (CW),which typically makes up about 50-55% of all the water in a refinery. Attimes CW can by-pass the WwTP to reduce its hydraulic loading, providedthe CW quality is appropriate for discharge. If contamination from aleak is detected then CW is rerouted back to the WWTP. In addition, CWmay be used for dilution of high-COD waters if they are otherwiseby-passing the WWTP.

Refinery Wastewater Treatment

Refinery wastewater quality varies significantly temporally according tothe process cycles. Its treatment is generally based on classicalactivated sludge treatment, usually with an initial flotation sequenceto remove the oil. The simplest flotation device is the AmericanPetroleum Institute (API) separator, the “workhorse” in any refinery forthe separation of oil/water and solids, which allows both settablesolids and large oil droplets (>150 μm) to be removed by up to 90%. Thisprimary step is then often followed by clarification. This may comprisecorrugated plate separators preceded by coagulation/flocculation andfollowed by either dissolved air flotation (DAF) or induced gas/airflotation (IGF/IAF). These technologies target much smaller oil droplets10-25 μm and reduce the suspended oil concentration to around 25-50mg/L.

Flotation, along with the increasingly employed electrocoagulationprocess, is most effective (in terms of % removal) for high suspendedoil concentrations, such as those arising in the desalter and BS&Weffluents. Such effluents, along with the spent caustic, also have aconsiderably higher salt content than the remaining effluent streams. Itis therefore desirable to treat these three streams separately from theremaining low-TDS streams to allow both pre-treatment for oil removaland segregated biological treatment of high-TDS effluent. Sincesegregation is rarely employed significant shock loads arise in refineryeffluents from dissolved salt and oil, in particular from sub-optimalelectrical coalescence (grid technology) or intermittent discharge ofthe mud wash from the desalter.

Whereas biological treatment of PW is still at the developmental stage,it is routinely employed for refinery and petrochemical effluents (Ishaket al., 2012) where the application of MBRs has also been explored(Rahman and Al-Malack, 2006; Qin et al., 2007; Viero et al., 2008;Zhidong et al., 2010; Di Fabio et al., 2013). Data reported from thesestudies (Table 0-2) have indicated organic contaminant removals,expressed as chemical oxygen demand (COD), generally in the range of84-99%, with fully optimised systems achieving >95% COD removal as wellas complete nitrification (Qin et al., 2007; Zhidong et al., 2009; DiFabio et al., 2013). Reported results indicate COD removals to varylittle with the hydraulic retention time (Scholz and Fuchs, 2000;Pendashteh et al., 2012), but strongly dependent on the feedwatercomposition and, in the case of nitrification, pH: a decrease in pHlevels to below 5.8 has been shown to reduce nitrification to as low as80% (Zhidong et al., 2009). Biotreatment may also be enhanced by theaddition of powdered activated carbon to the bioreactor, which helpsretain the dissolved organic matter and thus extend the treatment time.

TABLE 0-4 Refinery effluent composition, mg/L (Diya'uddeen et al., 2011)pH¹ COD BOD O&G SS NH₃ Phenol S² ⁻ Reference 7.0 300-600 150-360 <50<150  15 — — Ma et al., 2009 8.0 80-120  40  23  23 — 13 — Abdelwahab etal., 2009 6.6 600 — 120 120 — — 890  El Nass et al., 2009 8.4 220 — — —— — 22 Alias & Büyükgüngör, 2008 6.5-7.5 170-180 — 420-650  420-650 — —— Saien & Nejati, 2007 — 300-800 150-350 100 100 — 20-200 — Al Zarooni &Eishorbagy, 2006 6.7 200 — — — 70  4 — Santos et al., 2006 8.0-8.2 850-1020 570 — —   5-21 98-130 15-23 Coelho et al., 2006 —  68-220 0-1— — 0.2-21 0.9-3.8  — Rahman & Al-Malack, 2006 8.1-8.9 510-910 — — — —30-31 — Jou & Huang, 2003 6.5 800 — 100 100 —  8 17 Demirci et al., 199710    81  8 — —   2.3 — — Ojuola & Onuoha, 1987 — 660-710 — — — 22 30 10Serafim, 1979 — 300-600 150-250 100-300² — — 20-200 World Bank Group,1999 ¹unitless, ²desalter effluent

Whilst biological treatment is the most common and cost effective methodfor organics removal employed at oil refineries, the required treatedwater, which for discharge is normally between 100 and 200 mg/L COD (Maet al., 2009; Santos et al., 2006), may be challenged by bothnitrification inhibition and by the biorefractory nature of the organicfraction. A loss of nitrification can arise both from a C:N imbalance orfrom toxicity. In such cases where biological treatment is challenged,advanced oxidation may be necessary (Coelho et al., 2006; Saien andNejati, 2007; Abdelwahab et al., 2009) and its implementation within thesector is becoming increasingly common.

Petrochemical effluents tend to be less challenging than refineryeffluents, due to their reduced recalcitrance and water qualityfluctuation. An exception is effluents containing Polyvinyl alcohol(PVA) from polyvinyl chloride (PVC) manufacture, which are relativelyresistant to biodegradation and thus require a high MLVSS (mixed liquorvolatile suspended solids) concentration and long treatment times. Thismakes such effluents very conducive to treatment by MBR technology,particularly in cases where spatial restrictions exist.

In a 2012 publication, Lin et al. reviewed various literature reports ofMBRs applied to the treatment of industrial wastewater. Lin et al.'sdescription of the MBR process includes the reactor configurationsillustrated in FIG. 1.

FT (Fischer Tropsch) Produced Water

The effluent produced from FT process contains dissolved organic matter(principally oxygenates such as alcohols, carboxylic acids, ketones,aldehydes) as contaminants. It results from the Fischer Tropsch (FT)reaction between CO and H₂, which generates water as a product alongwith long, straight chain (alkanes) hydrocarbons (syn-crude). Inorganicminerals and nitrogen are at low levels, and other minor contaminantscomprise BTEX benzene, toluene, ethyl-benzene and xylene and alkanes(hydrocarbon oil).

Few studies have been conducted of efficacy of biological treatment ofFT produced water, and almost none using MBR technology. Evidence frompublished studies (Table 3-1) suggest that the effluent is highlybiodegradable with >99% removal of chemical oxygen demand (COD)attainable from feedwaters containing as much as 2,000 mg/L COD.However, operation and maintenance data, sludge characterisation, andoverall information pertaining to process efficacy is scant.

In WO 03/106351, Sasol Technology described a method purifyingFischer-Tropsch derived water. This method comprises a first step ofanaerobic digestion, followed by increasing pH in the range of between5.5 and 9.5 during a second step of aerobic treatment in an MBR. Furtherpurification may be conducted in a tertiary treatment stage anddissolved salts are removed to produce the purified water. This processis too lengthy, expensive and energy consuming.

SUMMARY OF THE INVENTION

In a first aspect, the invention provides a method of treating waterproduced by a Fischer-Tropsch (FT) process, comprising: obtaining waterproduced by a Fischer-Tropsch process having a pH of 5.0 or less andhaving carboxylic acids and alcohols dissolved in the water; addingsufficient alkalinity to the water to ensure that the pH of the water isin a range of 4.2 to 5.8; adding at least a portion of the water havinga pH in the range of 4.2 to 5.8 to a MBR wherein the water is treatedwith oxygen by aeration in the presence of bioorganisms to reduce theconcentration of organic carbon in the water, thus resulting in purifiedwater; and removing at least a portion of the purified water from theMBR.

In various preferred embodiments, this inventive method can have one orany combination of the following additional features: conducting the FTprocess in a fixed-bed reactor with cobalt-based catalyst; conductingthe FT process with a short contact time in the range of 50-2,000milliseconds; conducting the FT process in a microchannel reactor;subjecting the water produced in the FT process to a stripping operationprior to the step of adding sufficient alkalinity (typically by addinghydroxide); wherein just prior to adding the sufficient alkalinity, thepH of the water is in the range of 2.0 to 4.1, or in the range of 3.5 to4.0; wherein the alkalinity comprises NaOH, or KOH, or Na₂CO₃ or K₂CO₃;wherein sufficient alkalinity is added to the water to ensure that thepH of the water is in a range of 4.5 to 5.5 or in the range of 4.7 to5.3; wherein the flow regime of the water through the MBR is mixed andnot principally (either as a function of residence time or by volume)plug flow; wherein the purified water resulting from the process can beused without reverse osmosis; wherein the purified water resulting fromthe process is used without reverse osmosis or any other furthertreatment, such as any further treatment to remove dissolved salt;wherein the process does not result in any salty brine; wherein thepurified water resulting from the process, without further treatment, isused to cool a process stream in a cooling tower; and/or wherein theprocess operates in a continuous operating mode with the addition ofnutrients and removal of excess sludge.

The purified water can be recycled for other uses in the facility,including adding the water as a component of the feed for reformingreactions (e.g. steam reforming, or autothermal reforming), steamcracking, saturation of gas streams, sent to a cooling tower for use asa process coolant stream, in irrigation, upgrading to boiler feed orused for other oil and gas production uses, including enhanced oilrecovery or fracturing oil or gas formations (fracking). Alternatively,the purified water may be disposed as waste water or sent to municipalwater treatment. The purified water may be further purified in apolishing step such as using activated carbon absorption. The inventionincludes use of the purified water in any of the applications mentionedhere.

Mixing for the MBR is preferably obtained by aeration, and/or,especially in tanks that are not round or cylindrical, stirring and/orrecirculation pumps. Plug flow is not desirable since it will create apH gradient that is harmful to the bacteria in the MBR. Preferably, thePeclet number for the complete mixing in a mixed reactor is be greaterthan 0.1, more preferably greater than 1, more preferably greater than10.

Typically, all of the water having pH adjusted to be in the range of 4.2to 5.8 is added to an MBR; and all of the water is removed from the MBRwith the pH range of 6.5 to 8.0. In some preferred embodiments, theprocess is conducted in a continuous fashion. In the inventive process,MBRs preferably include an aerobic reactor and membrane(s) to trapsolids.

The invention also includes an aqueous composition made by the processdescribed above. The total dissolved salts in the aqueous composition(typically a stream) are typically in the range 100 to 300 mg/l.

In another aspect, the invention provides an aqueous composition,comprising TDS of 100 to 300 mg/l; 90 mass % or more of the dissolvedsalts are sodium bicarbonate or potassium bicarbonate; TSS of less than5 mg/l; TOC of less than 10 mg/l; COD of less than 50 mg/l; 30 minutechlorine demand of less than 5 mg/l; pH in the range of 6.5 to 8.0;hardness of less than 50 mg/l as CaCO₃; and wherein the carbon in theaqueous composition is significantly derived from fossil sources asdetermined by having a 14C/12C ratio that is 1.0×10⁻¹² or less,preferably 0.6×10⁻¹² or less. Measurements for these variables areeither described in this specification and/or well known andcommercially available.

The aqueous solution preferably contains 50 mg/l or less of alkali or 40mg/l or less of alkali, in some embodiments, in the range of 10 to 50mg/l, or in the range of 20 mg/l to 40 mg/l. In some embodiments, theaqueous solution has 150 to 300 mg/l TDS. In some embodiments, theaqueous solution has a TSS of 0.1 to 5 mg/l, or 1 to 5 mg/l. In someembodiments, the aqueous solution has a TOC of 1.0 to 10 mg/l; or 2.0 to8 mg/l; preferably comprising alcohols, carboxylic acids andpolysaccharides. In some embodiments, the aqueous solution has a COD of1.0 to 50 mg/l; or 5.0 to 50 mg/l; or 2.0 to 40 mg/l; or 1.0 to 15 mg/lor 5.0 to 15 mg/l. In some embodiments, the aqueous solution has ahardness of 1 to 50, or 5 to 50, or 2 to 40 mg/l as CaCO₃. In someembodiments, the aqueous solution has a chlorine demand of 0.1 to 5mg/l, or 0.5 to 5 mg/l.

These compositions (mentioned above) may result from the methods of thepresent invention.

These aqueous compositions are suitable for use as cooling tower make-upafter dosing with biocides such as chlorine, and corrosion inhibitors,as per normal operation of cooling water systems. No further removal ofTOC or TDS is required, and the low TDS of the treated effluent allowsthe cooling tower to operate with numerous cycles of concentration, upto a maximum of 12. The low concentration of organics on the effluenthelps reduce the growth of biofilms on the cooling system packing andpipework.

In a further aspect, the invention provides a method of purifying watercreated via Fischer-Tropsch synthesis, comprising: providing a firstvolume of FT produced water having a COD of at least 4000; passing theFT produced water into a stripper where the water is contacted with avapor or gas that removes an organic fraction into an overhead stream(118) which is cooled to condense an overhead liquid stream; and b)separating the overhead liquid stream into a distillate product stream(124) and a reflux stream (125) and the distillate product stream andthe reflux stream have the same composition; or condensing the effluentfrom the top of the stripper in a condenser (118) to form a liquidwherein the liquid phase condensed in the condenser is a single phase;and passing the bottoms liquid fraction (126) to further processing.

In various preferred embodiments, the invention can have one or anycombination of the follow features: wherein the distillate productstream and the reflux stream have the same composition; wherein theproducts from the stripper are limited to a distillate product stream, abottoms liquid fraction and, optionally, a vapor overhead fraction;wherein the recovery of alcohols in the distillate product stream isgreater than 90% (or greater than 95%) of the alcohols in the feedstream (112); wherein the alcohol content in the bottoms liquidfractions is less than 100 ppm (or less than 50 ppm); wherein thestripping is accomplished by the addition of live steam (116); whereinthe bottoms liquid in the stripper is indirectly heated with a reboiler;comprising passing at least a portion of the bottoms liquid fraction(126) from the stripper to an MBR wherein microorganisms consumeorganics in the water, and removing a second volume of purified waterfrom the MBR; wherein the second volume is at least 90% of the firstvolume and wherein the purified water has a COD of 50 mg/L or less,preferably 1 to 15 mg/L, or 5-15 mg/L; wherein the process steps consistessentially of providing a first volume of FT produced water having aCOD of at least 4000; passing the FT produced water into a stripperwhere the water is contacted with a vapor or gas that removes an organicfraction into an overhead stream (118) which is cooled to condense anoverhead liquid stream; and (b) separating the overhead liquid streaminto a distillate product stream (124) and a reflux stream (125) and thedistillate product stream and the reflux stream have the samecomposition; or condensing the effluent from the top of the stripper ina condenser (118) to form a liquid wherein the liquid phase condensed inthe condenser is a single phase; and passing at least a portion of thebottoms liquid fraction (126) from the stripper to an MBR whereinmicroorganisms consume organics in the water, and removing a secondvolume of purified water from the MBR; wherein the second volume is atleast 90% of the first volume and wherein the purified water has a CODof 50 mg/L or less, preferably 1 to 15 mg/L, or 5-15 mg/L; where the FTproduced water is made in a process comprising: passing syngas into afixed bed, Co catalyst-containing FT reactor at a contact time in therange of 50-2,000 ms, preferably 100-500 ms, and a temperature in therange of 170-230 C (or 180-220 C; or 190-210 C), preferably where thefixed bed is operated isothermally, within a 5 C (2 C) temperaturedifferential; wherein the pH of the bottoms liquid fraction is adjustedto a pH in the range of 4.5 to 5.5 prior to addition to the MBR; wherepH is adjusted by addition of NaOH or KOH; wherein a nutrient mixcomprising: N, Mo, Cu, Co, Ni, Mn, Zn, Fe, P, Mg, K, S, and Ca is addedto the MBR; and wherein purified water is removed from the MBR in a pHrange of 6.5 to 8.0

In any of the inventive methods, the FT produced water comprises one orany combination of the following characteristics: an alcohol to acidmolar ratio of at least 15:1, or at least 25:1, or in the range of 15:1to 200:1, or 25 to 250, or 25 to 200; or 25 to 100; or 30 to 70; and/orwhere the combined mass of methanol and ethanol comprises at least 70%,or at least 80%, or in the range of 70 or 75 to about 90% of the totalmass of C1 to C10 mono-hydroxy alcohols; or where the combined mass ofmethanol and ethanol comprises at least 50%, or at least 60%, or in therange of 60 or 65 to about 85% or 90% of the total mass of thefollowing: acetone, methyl ethyl ketone, diethyl ketone, benzene,toluene, xylenes, styrene, acetaldehyde, formic acid, acetic acid,propionic acid, butyric acid, valeric acid, hexonoic acid, methanol,ethanol, propanol, n-butanol, n-pentanol, n-hexanol, n-heptanol,n-octanol, n-nonanol, and n-decanol; or where the combined mass ofmethanol, ethanol and propanol comprises at least 55%, or at least 65%,or in the range of 70 or 75 to about 85% or about 90% of the total massof the following: acetone, methyl ethyl ketone, diethyl ketone, benzene,toluene, xylenes, styrene, acetaldehyde, formic acid, acetic acid,propionic acid, butyric acid, valeric acid, hexonoic acid, methanol,ethanol, propanol, n-butanol, n-pentanol, n-hexanol, n-heptanol,n-octanol, n-nonanol, and n-decanol. It is believed that we havediscovered that these characteristics make the water compositionsparticularly amenable to simple stripping operations. For example, thereis no need for a heavy alcohol side-draw (propanol or butanol andheavier) that would otherwise phase split from the aqueous phase in thestripper tower.

In any of these characteristics, the amounts of alcohols and acids arebased only on compounds containing 10 or fewer carbon atoms, which, inany case, make up the vast majority of moles of alcohols and acids inthe water phase.

In another aspect, the invention provides a method of purifying watercreated via Fischer-Tropsch synthesis, comprising (or consistingessentially of): providing a first volume of FT produced water having aCOD of at least 4000 and any characteristic or combination ofcharacteristics mentioned above; passing the FT produced water into astripper where the water is contacted with a vapor or gas that removesan organic fraction into an overhead stream (118) which is cooled tocondense an overhead liquid stream; and passing at least a portion ofthe bottoms liquid fraction (126) from the stripper to an MBR whereinmicroorganisms consume organics in the water, and removing a secondvolume of purified water from the MBR; wherein the second volume is atleast 90% of the first volume and wherein the purified water has a CODof 50 mg/L or less, preferably 1 to 15 mg/L, or 5-15 mg/L.

As is conventional, the phrase “consisting essentially of” means thatthe method does not include additional steps that materially affect theclaimed process. For example, in this case, this means that the processdoes not include a separate evaporator treatment, or a side draw fromthe stripper, or a series of strippers or MBRs.

Glossary

LIST OF ABBREVIATIONS AMS Ammonium sulphate API American PetroleumInstitute BS&W Bottom sediment and water normally bulk solids and water(in oil) BTEX Benzene, toluene, ethylbenzene, xylene COD Chemical oxygendemand TOC Total organic carbon TDS Total dissolved solids CW CoolingWater DO Dissolved Oxygen F:M Food to micro-organism mass ratio FTFischer Tropsch GTL Gas to liquids HRT Hydraulic retention time KOHPotassium hydroxide MBR Membrane bioreactor iHF Immersed hollow fibreiFS Immersed flatsheet MLSS Mixed liquor suspended solids NaOH Sodiumhydroxide PVA Polyvinyl alcohol PVC polyvinyl chloride RO Reverseosmosis PW Produced Water SRT Sludge retention time TSS Total suspendedsolids WWTP Wastewater treatment plant WAS Waste activated sludgeGAC is granulated activated carbon.FCV is fluid control valve.TPH is total petroleum hydrocarbons

The term “contact time” refers to the volume of the reaction zone withinthe microchannel reactor divided by the volumetric feed flow rate of thereactant composition adjusted to a temperature of 0° C. and a pressureof one atmosphere.

Stripping is a process in which a vapor or gas stream is contacted witha liquid process fluid in order to selectively decrease theconcentration of (and/or recover) one or more solutes in the processfluid. Typically, the recovered solutes comprise gases or compounds thathave relatively high solubility in the stripping gas(ses). Preferably,this contacting is conducted in a vessel with packing or trays, and maybe conducted with counter-current contacting of the vapor and or gaswith the liquid process fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of some MBR reactor configurationsthat could be used in the present invention.

FIG. 2 is a simplified flow diagram for processing FT produced wateraccording to some embodiments of the invention.

FIG. 3 is a schematic diagram of the apparatus for conducting the firstexample.

FIG. 4 illustrates a schematic diagram of the apparatus used in thepilot plant example.

FIG. 5 illustrates COD removal rate (generally upper data pointsconnected by a continuous line) and MLSS (Mixed liquor suspended solids)shown in the generally lower and discontinuous line.

FIG. 6 illustrates COD removal rate (generally upper data pointsconnected by a mostly continuous line) and MLSS (Mixed liquor suspendedsolids) shown in the generally lower and more discontinuous line.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates examples of conventional MBR systems that may beemployed in the present invention. In typical operation, water to bepurified (2) and air or oxygen (4) pass into reactor (6) where air (oroxygen) bubbles (8) pass through the water. Process control isschematically indicated at (10). In a side-stream configuration (top),water is pumped (12) through an external membrane module (14) andpurified effluent (16) passes out of the MBR system. In the immersedconfiguration (middle) a membrane module (18) is immersed within thesame vessel as the bubbler (20). In the airlift configuration (bottom),water from the first reactor (26) is passed to second reactor (28)containing membrane module (30). In the airlift system flow is(optionally) circulated between the reactors.

A flow diagram of an overall process (100) is illustrated in FIG. 2. Tobegin the process, syngas (102) passes into a Fischer-Tropsch reactor(104) producing organic liquid and solid products (106), tail gas (108)(which may be recycled (110)) and FT produced water (112). The FT wateris stripped in stripper (114) in which a stripping vapor or gas (116)contacts the water (112) and the overhead stream passes out of the topof stripper 114 and flows through a condenser (118) which is used tocool and either completely or partially condense the overhead stream.The stream then passes into optional reflux drum 123 where vapor (ifpresent) may optionally be removed via outlet 131. In preferredembodiments the condensed liquid is a single liquid phase and remains asingle liquid phase in the reflux drum. The condensed fraction of theoverhead stream is divided into a reflux stream (125) and a distillateproduct containing water and at least some of the stripped organics(124), which can be sent for further separation or recovery of products.The reflux stream is recycled to the stripper. The stripped water, orbottoms fraction of the stripper (126), can then be passed to the MBR,with or without further treatment in a dissolved air separation (DAF)process for oil removal. Nutrients (128, 129) and alkaline agent(typically sodium or potassium hydroxide) (130) can be added to thestripped water either before and/or after addition to the MBR. Cleaningfluid (132) can be passed into the reactor (typically taking one trainout of service for cleaning) and removed (134). Purified water (136)exits the system for any desired use.

In some preferred aspects of the invention, some or all of the watercreated in the FT process is subjected to a stripping operation. In somepreferred aspects, the stripper pressure is slightly above atmosphericpressure and the temperature of the mixture at any point in the columnwill be at the mixture bubble point. In some preferred aspects, thestripping can be done by flowing the FT water down a column with packingor trays, with the stripping fluid (e.g. injection of live (i.e.,pressurized) steam, nitrogen, air, or other available gases or vapour)in counter-current contact. Alternatively, heat may be supplied to thestripper by reboiling a portion of stripped water. Alternatively, or inaddition, the water could be distilled; however, stripping is preferred.The stripping may be done under vacuum or slightly above atmosphericpressure (for example, 0.1-10 atm). The temperature will be below theboiling temperature of the FT water. The mass ratio of stripping mediumto FT water may be 0.001 to 0.5, more preferably 0.01 to 0.2.

Water created in an FT process conducted at contact times of 5 secondsor less, more preferably 2 s or less or is or less and/or shortdiffusion distances (e.g. FT catalyst coating thickness of 100 μm orless, or FT catalyst particle size of 1,000 microns or less, or lessthan 500 microns or less) can be superior to water created byconventional FT or many other industrial waste water compositions.Advantages of the created water obtained as described herein may includeone or more of the following features: very low concentration ofaromatics (e.g., 10 ppm or less); low aldehyde concentration, andwherein the carbon present in the water is nearly exclusively (e.g., atleast 90% by mass, or at least 95% by mass, or at least 98% by mass, orat least 99% by mass) in the form of biodegradable acids (e.g., formic,acetic, propionic, n-butyric, n-valeric, and caproic), or alcohols(e.g., methanol, ethanol, propanol, butanol, decanol).

FT processes that are conducted in microchannels comprising an FTcatalyst and/or at short contact times with an FT catalyst areespecially desirable since such processes result in a superior mix ofcomponents dissolved in the FT produced water as compared toconventional FT processes. Further, the mixture of oxygenated species inthese short contact time FT processes enable simple water treatmentusing this invention without requiring the need for stripping columnsrequired for more difficult separations. The FT produced water in thisinvention may be processed in a simple stripper which does not requireeither (1) a side draw of vapor or liquid from the stripper or (2)liquid-liquid phase separation of the condensed overhead stream. Thestripper may be operated such that the composition of the distillateproduct is the same as the composition of the reflux. For purposes ofthe present invention, a microchannel is defined as a channel having atleast one internal dimension of 10 mm or less; in some preferredembodiments 5 mm or less. In preferred embodiments, the FT reaction isconducted through a planar array of microchannels that are adjacent to aplanar array of coolant channels. Short contact times are preferablyless than 5 second, more preferably less than 500 msec, and in someembodiments in the range of 150 to 500 ms.

While this process is useful for microchannel reactors, the methodsprovide significant advantages for any FT process, whether using aconventional reactor or not. There is a particular advantage forsmall-scale facilities that produce 15,000 barrels per day (BPD) orless, preferably 5000 BPD or less, of FT liquids and solids. The reasonfor this advantage is that at the small scale of the facility, scalingdown prior art waste water treatment processes is difficult and costly.There is a need to have a very simple waste water treatment process thatcan be built using modular construction. The stripper and the membranereactor and associated equipment can be built on modular structures inseparate facilities and transported to the site by truck, rail, orshipping. These systems can be used to avoid construction associatedwith conventional waste water treatment processes, such as waste waterponds using concrete structures or in-ground retention ponds withliners. For these reasons, the invention is also useful for treating FTwater for grass-roots facilities or facilities in remote locations whereit is difficult to integrate the waste water treatment with existingfacilities, such as an existing refining waste water treatment facility.Thus, the invention includes modular components for the FT processand/or water treatment including the MBR and other components. Theinvention also includes a kit for transporting the modular components.With this in mind, the invention is useful for any FT reactor type,whether conventional (slurry or fixed bed) or a new technology such ascompact, structured reactors, including microchannel reactors.

The Fischer-Tropsch Process

Examples of Fischer-Tropsch processes suitable for use in the presentinvention are described in U.S. Pat. Nos. 9,023,900, 7,935,734 USPublished Patent Application No. 2014/0045954 and WO2012107718 which areincorporated herein by reference. The following are some non-limitingdescriptions of some preferred embodiments of the FT process that can beused for creating water in conjunction with the present invention.

Suitable apparatus for conducting the FT process is known in the priorart. Preferred apparatus are microchannel reactors. A microchannelreactor may be made of any material that provides sufficient strength,dimensional stability and heat transfer characteristics to permitoperation of the desired process. These materials may include aluminum;titanium; nickel; platinum; rhodium; copper; chromium; alloys of any ofthe foregoing metals; brass; steel (e.g., stainless steel); quartz;silicon; or a combination of two or more thereof. Each microchannelreactor may be constructed of stainless steel with one or more copper oraluminum waveforms being used for forming the channels. In preferredembodiments, the FT reactor is not a fluidized bed reactor.

The FT reactor may comprise a plurality of plates or sheets in a stackdefining a plurality of Fischer-Tropsch process layers and a pluralityof heat exchange layers, each plate or sheet having a peripheral edge,the peripheral edge of each plate or shim being welded to the peripheraledge of the next adjacent plate or shim to provide a perimeter seal forthe stack. Some preferred construction techniques are shown in U.S.application Ser. No. 13/275,727, filed Oct. 18, 2011, which isincorporated herein by reference.

The FT reactor may be constructed using waveforms in the form ofcorrugated inserts. These corrugated sheets may have corrugations withright-angles and may have rounded edges rather than sharp edges. Theseinserts may be sandwiched between opposing planar sheets or shims. Inthis manner the channels may be defined on three sides by the corrugatedinsert and on the fourth side by one of the planar sheets. The processmicrochannels as well as the heat exchange channels may be formed inthis manner. FT reactors made using waveforms are disclosed in U.S. Pat.No. 8,720,725, which is incorporated herein by reference.

The FT reactor may comprise at least one process channel in thermalcontact with a heat exchanger, the catalyst being in the processchannel. The reactor may comprise a plurality of process channels and aplurality of heat exchange channels, the catalyst being in the processchannels.

The catalyst is preferably in the form of particulate solids. Theseparticulates can be packed into parallel arrays of small channels(typically having a width and/or height dimension of 1 cm or less,preferably 1 mm to 1.0 cm, and any length, for example lengths of 50 cmor 1 m or greater) that are interleaved with parallel arrays of heatexchange channels. Alternatively, the catalyst may be coated on interiorwalls of the process channels or grown on interior walls of the processchannels. The catalyst may be supported on a support having a flow-byconfiguration, a flow-through configuration, or a serpentineconfiguration. The catalyst may be supported on a support having theconfiguration of a foam, felt, wad, fin, or a combination of two or morethereof. The catalyst may comprise a coating on a monolith, includingmonoliths that may be separately inserted or removed from the reactor.

In one preferred process for conducting a Fischer-Tropsch reaction, areactant mixture in a reactor flows in contact with a catalyst to form aproduct comprising at least one higher molecular weight hydrocarbonproduct. Preferably, the catalyst is derived from a catalyst precursorcomprising cobalt, optionally a promoter such as Pd, Pt, Rh, Ru, Re, Ir,Au, Ag and/or Os, and a surface modified support, wherein the surface ofthe support is modified by being treated with titania, zirconia,magnesia, chromia, alumina, silica, or a mixture of two or more thereof.FT processes with short contact times are enabled by high cobaltcatalyst loadings, such as catalyst with greater than 20 mass %, morepreferably greater than 25%, 35%, or greater than 50 mass % cobaltloading. The product further comprises a tail gas, and at least part ofthe tail gas can be separated from the higher molecular weighthydrocarbon product and combined with fresh synthesis gas to form areactant mixture, the volumetric ratio of the fresh synthesis gas to thetail gas in the reactant mixture being in the range from about 1:1 toabout 10:1, or from about 1:1 to about 8:1, or from about 1:1 to about6:1, or from about 1:1 to about 4:1, or from about 3:2 to about 7:3, orabout 2:1; the reactant mixture comprising H₂ and CO, the mole ratio ofH₂ to CO in the reactant mixture based on the concentration of CO in thefresh synthesis gas being in the range from about 1.4:1 to about 2:1 orfrom about 1.5:1 to about 2.1:1, or from about 1.6:1 to about 2:1, orfrom about 1.7:1 to 1.9:1.

In some preferred embodiments, all water produced in the FT process iscollected in a separator, vessel, or tank, and the full flow issubjected to stripping, prior to subsequent use and/or treatment in anMBR.

The MBR reactor should not be configured with long stretches of plugflow. This is because, in plug flow, the pH will rise as the acids areconsumed by the microorganisms. Instead, mixing should be permitted suchthat pH remains similar throughout the MBR's volume. In one embodiment,a MBR can be run with a F:M of 0.05 to 0.5, a sludge age of 5 to 50days, a pH in the range of 5 to 9; a temperature in the range of 20 to40 C, and a conductivity of 50 to 1500 μS/cm.

Except for the specified conditions mentioned herein, conditions in theMBR are conventional. For example, the membranes can be removed andwashed with dilute sodium hypochlorite, as is conventional in the art.Microorganisms can be sourced from any municipal or industrial activatedsludge plant. The bacteria will adapt over time to the feed source, andproduce a simple, readily biodegradable waste which is suitable for mostheterotrophic and indeed autotrophic bacteria. There is no need for aspecial source of microbes. Preferably, the MBR should be run at steadystate conditions meaning constant feed rate, constant sludge age,constant pH and so on; avoiding large swings in operating conditions.

The overall process is typically considered to be continuous, but intypical commercial operation, plural MBRs will operate in parallel, andeach MBR will be brought down from time-to-time for cleaning of themembranes. During this period, the total flow will be accommodatedwithin the online MBR's, although at slightly higher hydraulic load.

Since the FT produced water lacks nutrients, nutrients will need to beadded for the microorganisms. In a preferred embodiment, nitrate,potassium, calcium, magnesium, manganese, sodium, iron, copper, zinc,molybdenum, nickel, and cobalt are added. For example, one preferrednutrient mix comprises ammonium nitrate, potassium nitrate, calciumnitrate, magnesium nitrate, manganese chloride, iron chloride, copperchloride, zinc chloride, nickel chloride, cobalt chloride and sodiummolybdate.

Examples

Described below is project aimed to establish the efficiency of treatingFT produced waterin an MBR. Two MBR pilot plants were employed, one fedwith an analogue and the other with FT produced water which was strippedof the volatile fraction. Both treatability (in terms of COD removal)and performance are assessed based on the COD removal and sustainableflux under different operating conditions.

1 Materials and Methods 1.1 FT Produced Water

Around 2000 L of FT produced water (Table 1-1) was shipped from pilotGTL facility in Ohio, US. Samples were collected from separators andcontained COD concentration of 25-30 g/l and pH 3.3. About 75% of theCOD is made up by methanol and ethanol.

The absence of minerals in the FT produced water, including nitrogen andphosphorus (N & P) demanded dosing with micro-nutrients to sustainbiomass growth (Tehobanoglous et al, 2004). For the smaller MBR pilotplant, a nutrient mix was prepared (Table 1-2) and blended the feedwater. For the larger plant, a commercial nutrient mix was used anddosed into the dilution water. Since there was no natural pH buffering,a small dose of caustic soda was added to the feed to provide a sodiumbicarbonate buffer in the bioreactor.

TABLE 1-1 FT produced water Composition Composition mg/L COD 30100 PH3.29 TOC 6600 DI-Ethyl- 181 Ketone Alcohols c1-c10 Butanol 446 Decanol5.4 Ethanol 2450 Heptanol 28 Hexanol 94.2 Methanol 7780 Nonanol 5.2Octanol 10.2 Pentanol 251 Propanol 690 Organic acids Acetic acid 261Propionic acid 20.4 Formic Acid 108 n-Butyric acid 22.8 n-Valeric acid23.6 Caproic acid 19.4 Aldehydes Acetaldehyde <10 Butyraldehyde <10Glutaraldehyde <10 Glutaraldehyde <10 Isobutyraldehyde <10Propionaldehyde <10 Formaldehyde <10 VOC Composition ug/L 2-Butanone8620 Acetone 52300 DEK 181 M,P-Xylene 8.3 Styrene 4.9 Strene 2.4o-Xylene 5.4

TABLE 1-2 SMBRs Nutrient Composition (mg/g dry solid) Composition mgComposition mg Composition mg N 104 Mn 0.1 K 12 Mo 0.0048 Zn 0.2 S 25 Cu0.024 Fe 2.4 Ca 12 Co 0.00048 P 21 Ni 0.001 Mg 8In some preferred embodiments, the nutrient composition can be definedas having each element within 50% to 200% of the concentrations shown inTable 1-2.Examples of FT produced water made using a short contact time FT processare shown in the Tables below:

TABLE 3 Example FT reaction water composition Component Units Normalload Peak load Acetone mg L⁻¹ 28 53 Methyl ethyl ketone mg L⁻¹ 5.0 8.7Diethyl ketone mg L⁻¹ 0.0 0.2 Benzene μg L⁻¹ 1.3 0.0 Toluene μg L⁻¹ 8.82.4 Xylene μg L⁻¹ 4.6 14 Styrene μg L⁻¹ 0.0 5.0 Acetaldehyde mg L⁻¹ 100.0 Formic acid mg L⁻¹ 78 108 Acetic acid mg L⁻¹ 478 261 Propionic acidmg L⁻¹ 86 20 Butyric acid mg L⁻¹ 76 23 Valeric acid mg L⁻¹ 76 24Hexanoic acid mg L⁻¹ 54 20 Methanol mg L⁻¹ 4038 7779 Ethanol mg L⁻¹ 19352450 Propanol mg L⁻¹ 460 690 n-Butanol mg L⁻¹ 232 446 n-Pentanol mg L⁻¹163 251 n-Hexanol mg L⁻¹ 80 94 n-Heptanol mg L⁻¹ 40 28 n-Octanol mg L⁻¹9.2 10 n-Nonanol mg L⁻¹ 5.8 5.0 n-Decanol mg L⁻¹ 0.0 5.4 TPH mg L⁻¹ 7.17.1

TABLE 4 Example FT reaction water composition Component Units Normalload Peak load Acetone mg L⁻¹ 28 53 Methyl ethyl ketone mg L⁻¹ 5.0 8.7Diethyl ketone mg L⁻¹ 0.0 0.2 Benzene μg L⁻¹ 0.0 1.3 Toluene μg L⁻¹ 2.48.8 Xylene μg L⁻¹ 4.6 14 Styrene μg L⁻¹ 0.0 5.0 Acetaldehyde mg L⁻¹ 0.010 Formic acid mg L⁻¹ 101 129 Acetic acid mg L⁻¹ 365 479 Propionic acidmg L⁻¹ 44 79 Butyric acid mg L⁻¹ 39 64 Valeric acid mg L⁻¹ 37 62Hexanoic acid mg L⁻¹ 26 41 Methanol mg L⁻¹ 8900 11782 Ethanol mg L⁻¹3088 3821 Propanol mg L⁻¹ 954 1411 n-Butanol mg L⁻¹ 593 803 n-Pentanolmg L⁻¹ 336 456 n-Hexanol mg L⁻¹ 118 154 n-Heptanol mg L⁻¹ 61 88n-Octanol mg L⁻¹ 20 31 n-Nonanol mg L⁻¹ 9.4 15 n-Decanol mg L⁻¹ 7.7 15TPH mg L⁻¹ 7.1 7.1Water compositions may be determined by GC/mass spectrometry or otherappropriate techniques. Care should be taken to avoid vaporizationduring sampling. It is believed that the values in Table 4 are moreaccurate than the values in Table 3.

1.2 Small MBR (SMBR) 1.2.1 Bench ScaleSetup

The small MBR (FIG. 3) had a nominal 4 L capacity tank and was fittedwith a single 0.1 m² flat sheet (FS) microfiltration (MF) membrane panel(Kubota, London, UK). The temperature of the MBR was controlled ataround 30° C. using a glass tube heater immersed in the water bath.Aquarium-style air stones were used to deliver 10 L/min of aeration toobtain a target minimum dissolved oxygen (DO) concentration of 2 mg/L asperiodically monitored using a Hach Lange LDO meter. Peristaltic pumps(Watson Marlow 101U/R) were used to deliver the feed water and nutrientmix as well as discharging of permeate, and were controlled manually.Control and monitoring of flow rate were performed manually.

The raw FT produced water was steam stripped prior to biotreatment toremove the bulk of the volatile organic carbon (VOC) and so reduce theorganic load for aerobic degradation. At full-scale this would beconducted using a packed tower stripper. At bench scale, the FT producedwater was boiled continuously at 100° C. for an hour to remove thealcohols, to reduce the COD concentration from 25-30,000 mg/L to around4000 mg/L. It was diluted with deionised water to achieve the desiredCOD level of 1000-5500 mg/L depending on the desired experimentalconditions. A COD of 1,000 mg/l was achievable with boiling alone, butthe loss of water by evaporation is high due to the extended boilingperiod. In a full scale steam stripping column, water loss is avoided bycondensing the stripper overheads. This was represented by simplydiluting the partially stripped water with deionised water (DI).Nutrient (Table 1-2) was dosed separately to avoid bacterial growth inthe feedstock.

The SMBR was seeded with 4 L activated sludge from a bioreactor (anindustrial SBR treating bottling plant wastewater) that had beenpre-acclimatised to FT produced water. During start-up the MLSSconcentration was increased to approximately 10 g/L. The operatingconditions were subsequently adjusted (Table 1-5) to sustain differentMLSS concentrations and F:M ratios of 0.19-0.3 d⁻¹. 0.3 to 0.19 fromthis project have little impact on the effluent quality and theoperation range from 0.17 to 0.32 have shown stability in the MBRperformance

TABLE 1-5 SMBR Operating Parameters Feed-COD MLSS HRT SRT FLUX mg/L mg/LF:M Hours Days LMH 2500 12000 0.1 40 50 1 5500 12000 0.3 35 50 1 400015000 0.2 30 50 1 3000 15000 0.25 12 35 3.5 2000 15000 0.3 12 35 3.52500 17000 0.3 12 35 3.5 1500 11000 0.25 12 20 3.5 1200 8500 0.25 12 203.5

1.3 Large MBR (LMBR) 1.3.1 Pilot Plant Set-Up

The LMBR had a nominal capacity of 150 L and was fitted with 5 flatsheet MF panels identical to that of the SMBR, providing a total area of0.5 m². The MBR temperature was controlled at ˜30° C. using a heatingjacket. A coarse bubble membrane tube air diffuser delivered 100 L/minto sustain a minimum DO of 2 mg/L, as monitored manually. The diffuserwas located at the base of the membrane cassette, to provide membraneair scouring of 12 Nm³/(h·m²) at 1001/min as well as provide oxygen forthe process. Peristaltic pumps (Watson Marlow 101U/R) were used to pumpthe feed and draw permeate as with the SMBR. A GAC polishing step wasincorporated based on 750 g of Norit GAC 1240 W (Steam activation ofcoal).

The SMBR feedwater comprised a combination of unstripped FT producedwater blended with acetic acid, the ratio of FT produced water to Aceticacid was 52:1, recycled permeate and a solution of commercial botanicnutrient (Miracle-Gro), diluted with 200 L of de-chlorinated potablewater. For the first 2 months, diluted unstripped FT produced wateralone was used as the feed source. After 2 months the feed wassupplemented by adding 9 kg of acetic acid and 2.5 kg of propionic acid,both reagent grade, and topping up with tap water. Unstripped FTproduced water with and without spiking was diluted to obtain therequired COD test concentration. Feed and nutrient were dosed from 2different tanks, and recycled permeate dosed directly back to the MBR,to avoid cross contamination causing bacterial growth. The LMBR wasseeded with activated sludge from a municipal WWTP with MLSS ofapproximately 7 g/L, and the MLSS subsequently gradually increased to 9g/L before adjusting further according to the experimental programme(Table 1-6).

TABLE 1-6 LMBR Operating Parameters Feed- COD MLSS F:M HRT SRT FLUX 20009000 0.2 18 NC 17 2000 12500 0.2 18 NC 17 2000 9000 0.2 25 36 11 200010000 0.2 25 30 11

1.4 Membrane Cleaning

Operation was sustained without routine chemical cleaning in place (CIP)and fouling behaviour observed with reference to the pressure, monitoredusing an analogue vacuum gauge on the pump suction line. Recoverycleaning was performed when the pressure reached 0.3 bar. Membranes werethen removed and washed at low pressure with mains water before applyingmechanical cleaning with a sponge and then soaking in 1000 mg/Lhypochlorite for 30 mins and then rinsing with deionised water.

1.5 Analytical Methods

The Chemical Oxygen Demand (COD) was tested using Merck's Cell Test andSpectroquant Photometer NOVA 60 according to Standard Methods (APHA,2005). Standard APHA methods were also used to estimate mixed liquorsuspended solids (MLSS), mixed liquor volatile suspended solids (MLVSS),total dissolved solids (TDS), Capillary Suction Time (CST) and chlorinedemand. The CST readings were obtained using Triton 2000 series CSTfilterability tester and Triton CST (7×9 cm) filter paper. Chlorinedemand was measured using Hach Colorimeter Filter Photometer incombination with Hach DPD Total Chlorine Reagent Powder Pillows,0.02-2.00 mg/L range.

The GAC isotherm determination employed GAC particles fractioned to32-106 μm in size at masses of 0.1, 0.5, and 1 g in a 120 mL volume ofSMBR permeate. The suspensions were shaken for 6 hours and the solutionsampled for residual COD.

As is well known, pH can be measured using conventional meteringapparatus and techniques.

3 Results and Discussion

3.1 Water Quality Vs. Retention Time

In the initial phase of SMBR operation the MLSS was allowed to increaseto a maximum of 18 g/L at an HRT of 32-42 h. During this period a steadyand gradual improvement of COD removal from 97% to 99% was observed whenoperation was stable (feed COD 3.1-3.9 g/L) and the MLSS between 14 and16 g/L. The SRT was decreased from 33 days to 20 days to reduce the MLSSto around 8.8 g/L. This resulted in deterioration in COD removal in theshort term (22 days) when operating conditions were being changed.However, on returning to steady-state operation of 20d SRT, 12 h HRT and1,000-1,200 mg/L COD feed the COD removal increased to >99%.

The LMBR MLSS was increased from 7 g/L to 15 g/L in first month ofoperation, with no sludge wastage up to 12.5 g/L MLSS at an HRT of 17.5h. During this initial period the COD removal rate was stable between97%-98% (FIG. 5). On decreasing the SRT to 20 days and increasing theHRT to 28 h on 15/07/14, the MLSS decreased to around 10.5 g/L and asignificant reduction in COD removal was observed. This coincided withthe spiking of the feed with acetic and propionic acids, significantlychanging the ratio of alcohols to acids in the feed such thatacclimation to the new feed conditions took 2-3 weeks. However, as withthe SMBR, the system recovered to produce 98% removal once steady-stateconditions had been re-established from 30 July onwards.

Overall COD removal of >99% was demonstrated for the stripped wastewaterfor steady-state conditions. This corresponded to a COD concentration aslow as 5 mg/L in the MBR-treated wastewater. The recorded COD removaldata from this study were in line with those from the two other reportedFT produced water treatment studies. They are considerably greater thandata reported for most of the bench-scale studies and full-scale plantoperation (Table 3-1), reflecting the benign nature of FT wastewatercompared with other O&G effluents which are generally much morechallenging (Table 0-2 and Table 3-1). The COD removal rate for thecurrent study meets the World Bank Group's industry guidelines of 150mg/L maximum COD (WBG, 2007) for petroleum industry effluents.

Operation of the MBRs was generally disrupted by malfunctions whichwould not be expected to arise in a full-scale plant. Foremost amongstthese was the clogging of the feedwater tubes of the SMBR in particular,causing significant fluctuation in the biotank sludge volume and MLSSconcentration. Clogging was caused by both the precipitation of ferricoxide—an unanticipated contaminant in the feedwater—and the formation ofbiofilms (including algal growth) associated with the nutrient feeddosing. An unusual facet of the biotreatment of the FT wastewater is thepH trend, where the treated wastewater is more alkaline than the feed.Whereas the feed wastewater pH was between 4 and 5, the treatedwastewater pH at steady-state (maximum COD removal) was around 8 for theLMBR and 7.5 for the SMBR. This is because the acidity generated by thecarboxylic acids in the feed is removed once the acids are degraded.

TABLE 3-1 Case studies Comparison on Petroleum Industry's MBR Parameterand Performance. COD Country/ Effluent Membrane Temp, Flux, SRT, HRT,MLSS, Feed, COD Company Region Scale Source Type ° C. LMH Days Hrs g/Lg/L Removal Reference Sinopec China Full Oil Refining, iHF 20- 8.9 30-15 3- 225 80% Judd, Guangzhou Ethylene Process 40 90 8 (min) 2014Petrochemical China Full Petrochemical iHF 15- 16 15- 0.33 6 2500 98%plant, Sichuan 30 30 (Max) Formosa, Yunlin Taiwan Full Oil Refining, iHF20- 20- NA NA 3.5 1000 95% Petrochemical 30 30 Syndial, Italy FullEthylene/ iHF NA 16- 15- NA 6 280 58% Porto Marghera PVC Process 19.8 30(min) Sangachal Azerbaijian Pilot Offshore Oil iHF 15- 13- NA NA 204000- 97% Rees et Terminal, Baku Reserviors 27 19.3 50000 (min) al.,2009 TPAO Basin, Turkey Bench PW iHF 20 10 30- 2.7^(b) 2- 1000- 67- Koseet Trakya “inf” 16 3000 83^(a) al., 2012 Petrochemical Singapore BenchPetrochemical iFS 26 10- 25 13- 8.6- 720- 85- Qin et plant 12.5 16 9.61590 95^(d) al., 2007 Petrobras oil Brazil Bench Refinery iHF ~25  15-“inf” 10.0 2.1- 400- 41- Viero et refinery 17.5 10.4 1050 67 al., 2008Queensland Energy Australia Bench Oil Shale Retort iFS 25 0.6 N/A 168-14- 10,000- 75- Lea et resources Sour Water 504 20 30,000 80% al 2013Sasol Technology, South Pilot GTL iFS 42 17 35 8 7.8 1800 96% Young etSecunda Africa al., 2006

3.2 Sludge Quality

SVI and CST were measured for the steady state mixed liquor. The SVI wasnot measurable, with no visible settling over a 2 hour period for eitherMBR. The LMBR had a mean CST of 316, ranging between 276 and 372 s overthe final 4 weeks of the study. The SMBR CST values variedsignificantly, progressively increasing from 109 s to 1064 s over thesame period. These values are significantly higher than those OF 5-50 sreported for FT produced water (Molipane et al., 2006) but are similarto those reported by Wu et al (2009) for Municipal sludge processed inthe simultaneous sludge thickening and digestion reactor. The high CSTand SVI values imply that thickening and dewatering of the sludge may besomewhat challenging (Fabregat et al, 2011).

3.3 Membrane Performance

Practical constraints of the study meant that the SMBR flux was very lowat −3.5 LMH, such that no fouling was observed for this MBR throughoutthe study. The LMBR was, however, designed to permit higher fluxes undermore representative operating conditions of 11-17 LMH, albeit with anextremely high membrane air scour rate of around 12 Nm³/(h·m²) comparedwith 0.2-0.8 normally associated with full-scale industrial effluenttreatment MBR plants, (Judd, 2014). This flux applied is in line withthe values listed in Table 3-1.

The LMBR membrane ran without cleaning for the first month, but thenrequired cleaning after each 7-11 day period of operation when thepressure increased to the threshold maximum value of 0.3 bar. Inspectionof the membrane showed that it had clogged (FIG. 3.3) in areas wherethere was insufficient aeration. Repositioning the membrane aeratorsignificantly ameliorated this problem and in the final 21 daysoperation at low pressure was sustained without necessitating cleaning.Note that the sludge layer adhering to the membranes was easily removedwith gentle water jets. It is clear that the limitations of the designof the module cassette holder contributed to the fouling.

3.4 Post-Treatment

Post-treatment using the GAC contributed only 0.35-1.45% to the totalCOD removal. The adsorption isotherm measurements indicated thatincreasing the concentration of GAC from 0.5 to 1 mg/L at the feedconcentration of 12 mg/L COD had no impact on the equilibrium CODconcentration of 6.4 mg/L COD±10%. It was therefore concluded that GACwas not a viable option for polishing residual dissolved COD, probablyreflecting the low molecular weight of the residual organic carbon.

The chlorine demand of the effluent was determined as being 0.4-0.46mg/L. This means that the water can be disinfected for use as coolingtower make up or other services without incurring excessive costs forchlorination.

DISCUSSION

-   -   For a high COD loading of up to 5500 mg/L a COD removal of over        98% was consistently achieved for both the real and analogue FT        produced water, somewhat higher than previously reported values        for petroleum industry wastewaters generally. This reflects the        highly biodegradable nature of this wastewater, in marked        contrast with other oil and gas effluents.    -   Significant fluctuations in the F:M ratio did not affect the COD        removal rate under conditions of progressively increasing the        MLSS concentration.    -   A flux of up to 14 LMH was sustained under operating conditions        of high but uneven membrane air scour applied despite an        extremely high sludge CST value of 275-372—indicating an        innately high sludge filtration resistance.    -   The low residual COD concentration of 5 mg/L or less attainable        under steady-state operating conditions means that the treated        effluent is suitable for re-use as cooling water following        moderate doses of chlorine (0.4 mg/L chlorine demand) without        requiring further polishing.    -   The use of a completely mixed reactor permitted partial        neutralisation of the feed with caustic soda, reducing the TDS        of the effluent and decreasing the blowdown (waste stream) from        its reuse for evaporative cooling.    -   MBRs would provide a lower-footprint process than the previously        applied membrane polishing process (classical activated sludge        followed by membrane filtration).    -   Although the previous patent literature disclosed that pH in the        MBR should be maintained between pH 5.5 to 9.5; surprisingly, we        discovered that excellent results could be obtained with a        relatively low pH of the water prior to addition to the MBR        (i.e., the water feed to the MBR). And the use of a lower pH        further improves the process by reducing or eliminating the        amount of brine that must be disposed. It was also surprising        that the pH increased in the MBR since in most industrial        wastewater plants, the pH goes down through the treatment        process.

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1-16. (canceled)
 17. An aqueous composition, comprising TDS of 100 to300 mg/l; 90 mass % or more of the dissolved salts are sodiumbicarbonate or potassium bicarbonate; TSS of less than 5 mg/l; TOC ofless than 10 mg/l; COD of less than 50 mg/l; 30 minute chlorine demandof less than 5 mg/l; pH in the range of 6.5 to 8.0; Hardness of lessthan 50 mg/l as CaCO₃; and wherein the carbon in the aqueous compositionis significantly derived from fossil sources as determined by having a14C/12C ratio that is 1.0×10⁻¹² or less, preferably 0.6×10⁻¹² or less.18. (canceled)
 19. The aqueous solution of claim 17 comprising 150 to300 mg/l TDS.
 20. (canceled)
 21. The aqueous solution of claim 19comprising a TOC of 1.0 to 10 mg/l; or 2.0 to 8 mg/l.
 22. The aqueoussolution of claim 17 wherein the organic compounds consist essentiallyof alcohols, carboxylic acids and polysaccharides.
 23. The aqueoussolution of claim 17 wherein the organic compounds comprise alcohols,carboxylic acids or polysaccharides.
 24. The aqueous solution of claim17 comprising a COD of 1.0 to 50 mg/l; or 5.0 to 50 mg/l; or 2.0 to 40mg/l.
 25. The aqueous solution of claim 17 having a hardness of 1 to 50,or 5 to 50, or 2 to 40 mg/l as CaCO₃.
 26. (canceled)
 27. A method ofpurifying water created via Fischer-Tropsch synthesis, comprising:providing a first volume of FT produced water having a COD of at least4000; passing the FT produced water into a stripper where the water iscontacted with a vapor or gas that removes an organic fraction into anoverhead stream (118) which is cooled to condense an overhead liquidstream; and b) separating the overhead liquid stream into a distillateproduct stream (124) and a reflux stream (125) and the distillateproduct stream and the reflux stream have the same composition; orcondensing the effluent from the top of the stripper in a condenser(118) to form a liquid wherein the liquid phase condensed in thecondenser is a single phase; and passing the bottoms liquid fraction(126) to further processing.
 28. The method of claim 27 wherein thedistillate product stream and the reflux stream have the samecomposition.
 29. The method of claim 27 wherein the products from thestripper are limited to a distillate product stream, a bottoms liquidfraction and, optionally, a vapor overhead fraction.
 30. The method ofclaim 27 wherein the recovery of alcohols in the distillate productstream is greater than 90% (or greater than 95%) of the alcohols in thefeed stream (112).
 31. (canceled)
 32. The method of claim 27 wherein thestripping is accomplished by the addition of live steam (116). 33.(canceled)
 34. The method of claim 27 comprising passing at least aportion of the bottoms liquid fraction (126) from the stripper to an MBRwherein microorganisms consume organics in the water, and removing asecond volume of purified water from the MBR; wherein the second volumeis at least 90% of the first volume and wherein the purified water has aCOD of 50 mg/L or less.
 35. The method of claim 34 wherein the processsteps consist essentially of providing a first volume of FT producedwater having a COD of at least 4000; passing the FT produced water intoa stripper where the water is contacted with a vapor or gas that removesan organic fraction into an overhead stream (118) which is cooled tocondense an overhead liquid stream; and b) separating the overheadliquid stream into a distillate product stream (124) and a reflux stream(125) and the distillate product stream and the reflux stream have thesame composition; or condensing the effluent from the top of thestripper in a condenser (118) to form a liquid wherein the liquid phasecondensed in the condenser is a single phase; and passing at least aportion of the bottoms liquid fraction (126) from the stripper to an MBRwherein microorganisms consume organics in the water, and removing asecond volume of purified water from the MBR; wherein the second volumeis at least 90% of the first volume and wherein the purified water has aCOD of 50 mg/L or less.
 36. The method of claim 27 where the FT producedwater is made in a process comprising: passing syngas into a fixed bed,Co catalyst-containing FT reactor at a contact time in the range of50-2,000 ms, preferably 100-500 ms, and a temperature in the range of170-230 C (or 180-220 C; or 190-210 C).
 37. The method of claim 36 wherethe fixed bed is operated isothermally, within a 5 C (or 2 C)temperature differential.
 38. The method of claim 34 wherein the pH ofthe bottoms liquid fraction is adjusted to a pH in the range of 4.5 to5.5 prior to addition to the MBR.
 39. The method of claim 38 where pH isadjusted by addition of NaOH or KOH.
 40. The method of claim 38 whereina nutrient mix comprising: N, Mo, Cu, Co, Ni, Mn, Zn, Fe, P, Mg, K, S,and Ca is added to the MBR. 41-42. (canceled)